Copper, chromium, arsenic compound for wood preserving



Patented Mar. 30, 1948 COPPER, CHROMIUM,

ABSENIG COMPOUND.

FOR WOOD PRESERVING William McMahon, Summit, at. 1., asslgnor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York No Drawing. Application December 31,1941,

Serial No. 425.125

This invention relates to preservative compositions for cellulosicmaterial. such as wood; and the present application constitutes acontinuation in part of my prior application, Serial No. 323,698, filedMarch 13, 1940 on Wood preservation, now abandoned.

The principal object of the invention is the provision of such apreservative composition that when applied to the cellulosic material itwill not only preserve the material but will also result in a treatedmaterial of high insulation resistance.

Another object of the invention is to provide a water-borne preservativewhich when applied to cellulosic material, such as wood, forms nowatersoluble salts.

A further object is to fix effectively and simultaneously in oneoperation compounds of copper, chromium and arsenic in wood or othermaterial containing cellulose and lignin while avoiding the formation inthe material of any permanently water-soluble salt.

In the preferred embodiment of the invention the wood preservativecomposition consists of an aqueous solution comprising chromic acid,arsenic acid and a compound of another metal such as copper, where thesaid copper compound consists of one or more of the following: copperhydroxide, copper carbonate, copper oxide, copper chromate, copperdichromate or copper arsenate. Copper dichromate is soluble in waterwhile the other copper compounds mentioned are soluble in an aqueoussolution of arsenic acid and chromic acid. Stated in a somewhatdifferent manner, the preferred composition comprises a Water-solublecompound of chromium, a compound of another metal such as copper, and ifdesired, a water-soluble compound of arsenic, where the compoundsselected are of such a nature that when the wood is impregnated with anaqueous solution of these compounds in the proper proportions thereaction of certain substances in the wood with the impregnatingsolution results in the formation of newcompounds, all of which arewater-insoluble.

The feature of having all of the reaction products water-insoluble is ofparticular importance in the impregnation of telephone poles Or othertimber having galvanized iron or other metallic members aiiixed thereto.If the reaction between the wood and the impregnating solution Claims.(01. 167-385) 2 is-such as to form a new salt which is water-soluble,the insulation resistance 01' the pole would be decreased by thepresence of such a compound; and if the new water-soluble compound is asalt. such as chloride or sulphate, the presence of such a salt wouldtend to accelerate corrosion of the pole line hardware.

For example, when an aqueous solution of chromium trioxide, copperhydroxide and arsenic pentoxide is injected into the wood the reactionof these compounds with the wood produces the following new compounds:chromium hydroxide, chromium arsenate, chromium chromate. copperarsenate, and copper chromate. All of these new compounds are insolublein water and hence none of the new compounds is of such a nature as toincrease the conductivity of the pole when subsequently exposed tomoisture or running water; and, further, none of these new compoundstends to accelerate the corrosion of any metallic article ailixed to thepole.

It has previously been proposed to employ certain chromium salts for thefixation of copper and arsenic in the wood to afford protection againstwood-eating insects and wood-destroying fungi, where the fixation isbelieved to be due to the reduction of the chromate ions by certainsubstances in the wood. The present invention in that respect is similarto'these earlier proposals but provides an improvement thereonparticularly for those uses of the treated timber which require theattachment of metal fixtures to the timber, such as the hardware usuallyemployed on telephone poles. Since the wood treated with the solution ofthis invention has a markedly higher electrical resistance than would bethe case if the reaction of the ingredients on the wood produced a.water-soluble by-product, it follows that the treated wood of thisinvention can also be advantageously used for poles for powertransmission lines and the like.

In the above description of the preferred compositions, certaincompounds of copper have been listed but, if desired, the correspondingcompounds of nickel, zinc, cobalt or barium may wholly or partiallyreplace the copper compounds. A further permissive variation is to omitthe arsenic compound entirely where the fungidestroying property 0!arsenic is not needed. It may also be noted that when the arsenic isadded aeaaau in the form of a metallic arsenate, the arsenic pentoxidemay be absent or present in a correspondingly reduced amount; while whenthe maior portion of the chromium is added in the form of a metallicchromate or dichromate it will still be advisable to add some chromiumtrioxide or its equivalent to produce chromic acid in the aqueoussolution.

The following data include several examples of the preferredcompositions of this invention and indicate in parts by weight theamount of each compound which is advantageous to employ. approximateupper and lower limits being given for each compound. In general, it maybe stated that in the preferred wood preservative compositions of thisinvention each of the elements, chromium. arsenic and copper or othersubstituted metal. is present insufflcient amount to exert a substantialtoxic action on wood-destroying organisms.

Example I Permissible Pren [erred Porto Arsenic pentoxide mam. 2E0) 5 to15 parts.-- 5 a t dmtasaw ma ".".-Z -12 .3; 3:: 800 to am a more parts.

where the copper hydroxide may be replaced wholly or in part by thechemically equivalent weight of one or more of the hydroxides of zinc,nickel,.cobalt orbarium. For example, if the copper hydroxide of ExampleI is wholly replaced by zinc hydroxide (Zn(OH) the permissible variationwould be 6 to 9 parts with 6 parts preferred; if replaced by nickelhydroxide (Ni(OH) 2) the permissible variation would be 5.5 to 8.5 partswith 5.5 parts preferred; if replaced by cobalt hydroxide (Co(OH)r) thepermissible variation would be 5.5 to 8.5 parts with 5.5 partspreferred; or if replaced by barium hydroxide (Ba(OH) 2.8H2O) thepermissible variation would be 19 to 29 parts with 19 parts preferred.

-11. desired, the copper hydroxide of Example I may be replaced by thechemically equivalent weight of any one of the other permissible coppercompounds, as indicated by the subsequent examples:

Example I! Preierrcd Parts Arsenic pentoxide (AssOaZHsO) Chromiumtrioxide (CrOs) gil copper carbonate [2CuC0;.Ou(0H);1.

'IOWtar by cobalt carbonate (C0003) the permissible I variation would be7 to 11 parts with 8 parts preferred; or if replaced by barium car onated (BaCOs) the permissible variation would be 12 to 19 parts with 18.5parts preferred.

Example III Permissible Pre- Variation ierred A ul 1 t as (A 0 211,0 e

rse c no e s chromiu r r trioxide (dr6r)..--- l5 Oupric oxide (OuO) 5Water permissible variation would be 4.5 to 7 parts with i 4.5 partspreferred; or if replaced by barium oxide (BaO) the permissiblevariation would be 9.5 to 14.5 parts with 9.5 parts preferred.

where the copper chromate may be replaced wholly or in part by thechemically equivalent weight of one or more of the correspondingchromates of zinc, nickel, cobalt or barium. For example, if the copperchromate of Example IV is wholly replaced by zinc chromate (ZnCrOa'IHaO)the permissible variation would be 18.5 to 28 parts with 18.5 partspreferred; if replaced by nickel chromate (NiCrOr) the permissiblevariation would be 10.5 to 16 parts with 10.5 parts preferred; ifreplaced by cobalt chromate (CoCrOi) the permissible variation would be10.5 to 16 parts with 10.5 parts preferred; or if replaced by bariumchromate (BaCrOu) the permissible variation would be 15 to 23 parts with15 parts preferred. It also is to be noted that when the chromate ofzinc, nickel, cobalt or barium is substituted for the basic copperchromate of Example IV, there is a slight change in the permissiblevariation of the chromium trioxide over the amounts given in Example-IV, namely that the permissible amounts of chromium trioxide wouldbecome 5 to 15 parts, with 10 parts preferred.

Example V Permissible Variation Parts Arsenic ntoxide (As O .28 0

cunnin trioxide 2036.).--)

Copper dichromate CuCnOMEhO) rowan where the copper dichromate may bereplaced wholly or in part by the chemically equivalent weight of one ormore of the dichromates of zinc,

Perierred nickel, cobalt or barium. For example, it the copperdichromate of Example V is wholly replaced by zinc dichromate (ZnCrzOr)the permissible variation would be 17 to 25.5 parts with 17 partspreferred: if replaced by nickel dichromate (2N1C12O1.3H2O) thepermissible variation would be 18 to 27.5 parts with 18 parts preferred;it replaced by cobalt dichromate (CoCrzOaHaO) the permissible variationwould be 17.5 to 26.5 parts with 17.5 parts preferred; or it replaced bybarium dichromate (BaCi'zOv) the permissible variation would be 21 to 32parts with 21 parts preferred.

where the copper arsenate may be replaced wholly or in part by thechemically equivalent weight of one or more of the arsenates of zinc,nickel, cobalt or barium. For example, if the copper arsenate of ExampleV1 is wholly replaced by zinc arsenate (Zn3(AsO4)2.8I-I2O) thepermissible variation would be 12.5 to 19 parts with 12.5 partspreferred; it replaced by nickel arsenate (Ni3(ASO4) 2.8H2O) thepermissible variation would be 12 to 18 parts with 12 parts preferred;if replaced by cobalt arsenate (Ca(ASO4)a.8I-I2O) the permissiblevariation would be 12 to 18 parts with 12 parts preferred; or ifreplaced by barium arsenate (Ba3(AsO4)z.3H2O) the permissible variationwould be 15 to 23 parts with 15 parts preferred.

In the event that it is desired to fix only a compound of copper but notof arsenic .in the wood the arsenic compound in the above examples maybe omitted entirely, so that Example I, for instance, would become:

Example VII Permissible variation Chromium trioxide (Cr 03) 10 to 20parts Copper hydroxide [Cu(OH)2] 5 to parts Water 300 to 3000 or moreparts where the chromium trioxide and the copper hydroxide arepreferably used in the ratio of 2 to 1 and where the copper hydroxidemay be replaced wholly or in part by the chemically equivalent weight ofone or more of the corresponding hydroxides of zinc, nickel, cobalt orbarium.

The following remarks, as specifically applied to Composition I, areoffered in explanation of the listing of preferred limits for thevarious ingredients employed in the wood preservative of this invention.As shown in Example I, the preferred limits for arsenic pentoxide areabout 5 to parts. Below about 5 parts the arsenic pentoxide is notpresent in suflicient amount to secure the desired efiectiveness in woodpreservation; while when substantially more than 15 parts are employedthe arsenic is not so permanently fixed in the wood, as is the case whenthe amount employed is within the desired limits, and there 15 Water 6would be an undesired'leaching oi the arsenic from the wood. Withrespect to copper hydroxide the same observations apply as for thearsenic compound. A minimum of about 6 parts of copper hydroxide isneeded to secure the desired effectiveness in wood preservation; andwhen substantially more than 9 parts of copper hydroxide are employedthe copper is not so permanently fixed in the wood as is the case whenthe amount employed is within the stated limits. The chromium compoundis needed to cause the fixation of the copper and arsenic in the wood.The lower limit of about 10 parts of chromium trioxide is needed tomaintain the arsenic and copper compounds in solution and precipitationwill occur if a substantially smaller amount of chromium trioxide isemployed. For the maximum amounts of the arsenic and copper compoundsgiven in Example I, any amount of chromium trioxide beyond about 20parts is unnecessary and superfluous in obtaining the desired fixationof the copper and arsenic compounds in the wood.

A composition of 5 parts arsenic pentoxide, 17 parts chromium trioxideand 6 parts copper hydroxide dissolved in 1000 parts of water has a pHvalue of 1.02.

The amount of water employed with the above compositions depends to someextent upon the type of treatment employed in impregnating the wood. Inthe full cell treatment, where the wood is first subjected to a partialvacuum and is then immersed in the solution under pressure for sometime, the amount of water for the above examples should be in theneighborhood of 1000 to 2000 parts. In the so-called empty celltreatment, where the wood is first placed under greater than atmosphericpressure to drive air into the wood, and is then immersed in thesolution under still greater pressure for a certain period of time,after which the wood is removed from the solution and placed under apartial vacuum, the solution employed should have a higher degree ofconcentration employing water in the neighborhood of 500 to 1000 parts.

It should be noted that the preservative composition of this inventioncan be safely used in iron or steel tanks or other wood-treatingequipment without any objectionable corrosive action.

Several fungicides for treating wood telephone poles including thesolutions of the present invention have been studied to determine theirrelative corrosiveness towards galvanized iron pole hardwarewith whichthey might come in contact. This was done by measuring the potential ofiron immersed in the respective solution with a tenth normal calomelreference electrode by means of a continuously recording potentiometerwhere the readings were taken over a period of fifty minutes. In thefollowing tabulation, solutions A and B are representative of thisinvention, while solutions C and D represent certain prior proposals.

Solution A consisted of:

Parts Copper hydroxide [Cu(OI-I)i] 10 Chromium trioxide (CrOa) 17 Water1000 Solution B consisted of: I

Parts Arsenic pentoxide (AszOs.2I-Iz0) 5 Copper hydroxide [Cu(OH)2] 6Chromium trioxide (CrOa) 1'7 aisas r:

Solution C was an aqueous solution. of certain compounds of arsenic,copper and chromium j where the compounds'were such, when used as 1 awood preservative, as to produce a water-solusulphate would be formed asa by-product in the reaction of the solution on the wood but difleredfrom solution by the omissionof arsenic and the addition of a smallamount of an organic acid.

its potential after fifty minutes exposure to the solution were asfollows:

Potential Initial Solution Potential fi zg g in-Volts Minute,

.4. --o.12s -0.o3 B. -o.a1 -o.a1s o. -o.scs -o.41o D -o.es -o.eo

From these data it is apparent that solutions A and B passivate the ironmore strongly than solutions C and D since the potential values forvsolutions A and B are more electropositive than solution is the onegiving the wood the higher,

insulation resistance. In thesetests of the insulation resistance,air-seasoned poles were treated with the various solutions and then'wereexposed in the open air for about eleven months before the followingmeasurements were taken, where the insulation resistance given is inmegohms per foot of test section length:

B 1. 7449 0 0.2053 D. 0.2603 Standard creosote treatment 0.6582

The preservative of this invention may be injected into the wood in a.variety of ways as by placing the wood under a partial vacuum and thenimmersing the wood in the solution under a pressure greater thanatmospheric'pressure; by the empty cell treatment previously described;or by dipping the wood in open-vessels containing the preservativesolution; or by brush or spray painting the wood with the solution.

After the preferred ingredients, arsenic pentoxide, chromium trioxide,and a copper compound such as copper hydroxide, are dissolved in water,

1 the resulting solution may be considered as one containing arsenicacid, .chromic acid and the copper compound; and hence, in the followingclaims any reference to chromic. acid or arsenic acid is also intended.to include the, oxide of chromium orarsenic.

copper are dissolved in water, the solution consists substantiallyexclusively of ions \of copper, ions of hydrogen, chromate ions,dichromate ions, and arsenate ions. It may also be noted that thecopper, nickel, zinc, cobalt or barium compound employed in the solutionof the present invention is preferably one in which the metal isdivalent.

WhatIclaimis:

1. A preservative for wood consisting of ingradients which. whendissolved in water, are capable of reacting with certain substances insaid material to form compounds which are all water-insoluble, saidingredients comprising chromium trioxide and a substantial amount of acopper compound the component of which, other than copper, is selectedfrom the group consisting of hydroxide, carbonate, chromate, dichromateand arsenate, said chromium trioxide being present in a substantialamount at least suilicient to maintain the metal compound in solutionwhen the ingredients are added to water.

2. A wood preservative consisting of ingredients which, when dissolvedin water, are capable of reacting with certain substances in the wood toform salts which are all water-insoluble, said ingredients comprisingarsenic pentoxide, chromium trioxide and a copper compound in woodpreserving amounts, the component of the copper compound other thancopper being selected from the group consisting of hydroxide, carbonate,chromate, dichromate andarsenate.

3. A wood preservative comprising an aqueous solution of arsenic acid,chromic acid and a copper compound which is insoluble in water but issoluble in a water solution of arsenic acid and chromic acid, thecomponent of said copper compound other than copper being selected fromthe group consisting of hydroxide, carbonate, chromate, dichromate andarsenate, said-arsenic acid,

chromic acid andcopper compound being present in suihcient amounts toexert a substantial toxic action on-wood-destroyin organisms.

4. A wood preservative consisting of an aqueous solution of chromiumtrioxide, copper hydroxide and arsenic pentoxide, where the ingredientsare present inthe following amounts by Weight: approximately 10 to 20parts of chromium trioxide, approximately 6 to 9. parts of copperhydroxide and approximately'5 to 15 parts of arsenic pentoxide.

5. A wood'preservative consisting of an aqua weight: about 10 to-20parts of chromium trioxide, about '1 to 11 parts of copper carbonate andabout 5 to 15 parts of arsenic pentoxide.

6. A wood preservative comprising by weight about 5 to 15 parts arsenicpentoxide, 10 to 20 parts chromium trioxide, and 6 to 9 parts copperhydroxide, where the amount of chromium trioxide employed is about twicethe combined amount of arsenic pentoxide and copper hydroxide.

'7. A wood preservative comprising by weight about 5 to 15 parts arsenicpentoxide, 10 to 20 parts chromium trioxide and 7 to 11 parts coppercarbonate, where the amount of chromium 7 further expl'anationflof v thelanguage employcdin some oftheappende'd. claims it may be noted that.When'arsenic pentox-' 'ide, chromium trioxide, and the oxide,hydroxide,

carbonate, chromate, dichromate or arsenate of.

trioxide employed is about twice the combined amount or copper carbonateand arsenic pentoxide.

8. An acidic impregnating solution for preserving wood which comprises acopper compound dissolved in an aqueous solution oi. arsenic acid andchromic acid, the component of the copper compound other than copperbeing selected from the group consisting of hydroxide, carbonate,chromate, dichromate and arsenate characterized in that when the wood isimpregnated with the said solution, all of the compounds formed by thereaction of the solution with the wood are insoluble in water.

9. An acidic impregnating solution for preserving wood which comprises ametal compound dissolved in an aqueous solution oi! arsenic acid andchromic acid, characterized in that said metal compound comprises copperhydroxide and "further characterized in that when the wood isimpregnated with said solution all of the compounds formed by thereaction of the solution with the wood are insoluble in water.

10. An acidic impregnating solution for preserving wood which comprisesa metal compound dissolved in an aqueous solution of arsenic acid andchromic acid, characterized in that said metal compound comprises coppercarbonate and further characterized in that when the wood is impregnatedwith said solution all of the com--- 5 pounds formed by the reaction orthe solution with the wood are insoluble in water.

WILLIAM MoMAHON.

REFERENCES CITED The following references are oi! record in the file ofthis patent: UNITED STATES PATENTS

